Pal artifacting in Altirra

[bfollett]

There is a discussion in the TI 99/4a programming forum where they are discussing clones of Parsec. The Atari clone I've attached was being discussed, and I told them that artifacting had to be turned on in the emulator to see the desired color effect of the programmer. Anyway, I've read that color artifacting is different on Pal vs NTSC, but when I tried changing Altirra to PAL with standard PAL artifacting, I basically saw no change to the display. Is that correct? I've attached the program and a few screen captures from Altirra. The 1st capture has no artifacting and you can see the ground is made of a bunch of vertical lines that would get transformed into colors when artifacting on a TV comes into play. The second capture is with NTSC artifacting turned on, and you see the added colors. The third is with PAL artifacting turned on and to me it looks the same as the no artifacting capture??? Is this to be expected with a PAL display?

 

Bob

 

Parsec XL.xex

[Synthpopalooza]

PAL artifacting is a different animal altogether. It has nothing to do with hi-res artifacts.

 

How it works is, in 192 scanline modes (Antic C, E, F, and Antic modes 2, 3, 4, and 7) the scan line below gets blended with the scanline above, to make a blended color. This is how modes like APAC, and that 16 color 160x96 Graphics 15 mode work. It doesn't look as good in NTSC, but on PAL it is the closest we can come to a non-flicker 16 color mode.

 

The best method is to have a color of about luminance 2 on the first line, then a greyscale luminance on the second line ... this is usually accomplished by either a DLI to change the color palette, or a DLI to shift the GTIA into Graphics 9.

[José Pereira]

Yes. It never works in a hi-res mode.

This Parsec like most the same type hi-res old ones were done to get the NTSC Artifacting.

What you should know:

-> NTSC only work in hi-res modes where you have one colour and that same colour in another luminance.

The artifacting gets you, normal, two more colours. This two more colours are only where's single hi-res pixels (that's why there, for example, on your screen, the vertical ground hi-res lines turned into green).

-> PAL: Never works with hi-res pixels (could but only if you have one scanline hi-res and the other 2:1 or 4:1 ratio). From here and from the great Synths explanation you get that the PAL gets the it by blending the colours on the 'before' scanlines.

 

For right we should call PAL Blending and NTSC Artifacting for obvious reasons.

[bfollett]

Ahhh, I didn't realize it was a completely different type of artifacting. So games that relied on artifacting like the pinball games just looked black and white with striping.

 

Bob

[José Pereira]

That's it.

See the great example of PAL Blending in GTIA GR.9 of NRV's ProjectM Wolfenstein 3D clone where one scanline has the 16colours in a very darker luminance and the below one has colour0 (black, all grays and white).

Get the files here on the A8/5200 Programming Forum and change the video settings on Altirra like you did between PAL and NTSC.

You'll see this and the way it works and why we should say that PAL it's a blending.

PAL put other colour because of the pixel colour you have in the 'closest' scanline.

On the other way NTSC produces new colours according to the position an hi-res pixel is more the CPU and TV clock same or multiples (A8 and Apple2 can produce NTSC Artifacting but C64 not).

On the other hand every computer will get PAL Blending because it's a T.V. stuff and no need to have a join of some factors between a computer machine and a television clock ratio like in NTSC.

[Rybags]

Artifacting in the NTSC sense can occur on A8 and C64 but is nowhere near as usable as NTSC due to the fact there's not that integer ratio between colour and pixel clocking.

 

Filled areas of constant colour don't occur, instead you get the banded appearance which AFAIK hasn't really ever been put to a practical use. Also I believe there are differences in results depending on machine type like with NTSC.

Edited August 25, 2013 by Rybags

[José Pereira]

Artifacting in the NTSC sense can occur on A8 and C64 but is nowhere near as usable as NTSC due to the fact there's not that integer ratio between colour and pixel clocking.

I was trying to say that.

Isn't it that because A8 clock or ANTIC can get the Artifacting that a C64 1Mhz can't?

(yes, I know that we still has the difference between different A8 Machines like the ones with GTIA and the older ones with CTIA, like green/pink or blue/brown for example.

Edited August 25, 2013 by José Pereira

[Synthpopalooza]

You can get PAL blending of a sort in Graphics 8.

 

Works like this: You need to alternate the scanlines between Yellow and Blue (that is chroma 1 and 9, or chroma 14 and chroma 8 ...) by changing PF2, the BG register for Graphics 8. Set PF1 (the pixel brightness) to a bright luminance like 14.

 

 

 

Use artifacting where you plot on odd pixels or even pixels to get purple-green artifacting ... the colors will be different than purple - green when placed on a blue or yellow background. Everywhere that you plot one of these colors, the pixel below it has to be a solid nonartifact pixel, so you will need to plot in both the even and odd column.

 

So, here's an example:

 

Blue line: 0 1

Yellow line: 1 1

 

The 01 artifact will blend with the bright yellow below to make a new color.

 

You can also do the same by plotting the artifact on the yellow line and the solid color on the blue line below.

 

 

This should get you about 16 colors, with a pseudo 160x192 resolution, but with the limitation that you can't plot artifacts next to solid colors. Also, plotting a double pixel in reverse order (0110 instead of 1100) slightly changes the color of the pixel as well.

 

Blue-Yellow works best because the colors are on opposite sides of the color wheel, and they augment real well with the purple-green artifacts present in most of the newer model XL/XE's. You can try other combos as well, like red-cyan, or purple-green, if your system uses blue-brown or red-blue artifacting instead of purple-green.

Edited August 25, 2013 by Synthpopalooza

[Synthpopalooza]

Also, back to PAL blending:

 

It doesn't work as well on NTSC, but this can be compensated for, by doing a scanline shift ... changing the first line of the display list between Skip 8 and Skip 7 scanlines to jitter the screen up and down a scanline 60 times a second. As you can do 60 frames a second (as opposed to 50 on PAL) the colors will blend a bit better.

 

Example for NTSC machines is in this post:

 

http://atariage.com/forums/topic/197450-mode-15-pal-blending/?p=2638213

 

Looks best on NTSC. PAL will flicker horribly.

[+CharlieChaplin]

Well,

 

I am living in Germany, I have only PAL Ataris and the tv connected to the A8 does only PAL. Nevertheless here is a picture of a PCS pinball, its a screenshot from my PAL TV and allthough the pinball uses Gr. 8 you can see some colours:

 

 

 

I see green, violet, red and brown (and a few other false colours) in the mines area - why ?

 

-Andreas Koch.

 

[José Pereira]

Some colours? That is f...ink amazing! What T.V. do you have?

Anyothers here ever get this or know how and why?

Here's also PAL and I don't remember to ever get anything like this on the old days on my now defunct machine.

What I remember is from the English magazines of the 80s we can see some screenshots (even the Sinclair ones) that on A8 those hi-res isometric games produces two colours artifacting in a similar way to the NTSC TVs but this time just red and green in vertical single hi-res lines and pixels according to they are placed in odd or even xPos.

I remember that we could saw this in Atari User games section when they revue Molecule Man and Head Over Heels.

If anyone have this issues and could scan them to post those screens here it would be great.

Andreas do you have these two games or can download them to post here what you get on your TV?

[Synthpopalooza]

Graphics 8 artifacting 101.

 

Because the average TV is unable to display hi-res modes (Graphics 0 and 8.) properly, artifact colors crop up. The color that shows up depends on whether you plot the pixel in an even or odd numbered column.

 

So for instance, 01 might return purple, 10 might return green, where as 11 will return the correct Graphics 8 pixel color. And doing something oddball like 0110 will make a sort of off-white color.

 

As mentioned above, Graphics 8 artifacts can also be altered by changing PF2 to a different color, and also by overlaying PMG's using GPRIOR setting of 0. This drastically increases the number of colors displayed in this mode.

 

As for the vertical banding ... no idea but it would be helpful to see this output on other machines.

 

EDIT: The game in question can be downloaded here: http://www.atarimania.com/game-atari-400-800-xl-xe-u-boot-das_27412.html

 

I just checked and no PMG's are being used here. But I think on PAL machines, there is another kind of vertical artifacting that occurs, but this happens on odd and even color clocks, and it varies the colors slightly. Check out this screenshot from Altirra, using a setting of PAL artifacting (High):

 

You can see just a slight color variation. Using this setting in Altirra you can't see the purple and green hi-res artifacts (you'd need to set the emulator for NTSC artifacting) but when these artifacts and the PAL artifacts are blended, you get all sorts of weird colors.

 

Edited August 26, 2013 by Synthpopalooza

[José Pereira]

Is it maybee Charlie has it TV settings too bright and colour bar at maximum? This would strenght the pixels, blend and mix, indeed mess all the colours but this would make sense if it's a colours picture not a black and white one that at a maximum would only show some 'here and there' colour small pixels.

I still want to see what he gets in Molecule Man and Head Over Heels.

And why not, just to see if it's his TV whats the looking he get on the PAL Blending GR.9 NRV's Project-M (also good to try underdstanding this weird looking would be a 2:1 ratio colourfull game like Henry's House).

[José Pereira]

I get it. Put Altirra in PAL Artifacting (High) and you get exactly what I said that saw on the magazines. Just load Molecule Man and it's exactly what I remembered.

But whats or why we have available the possibility to set (High) for NTSC and PAL Artifactings? Is it related/because of some TV's brands, what we choose in our TVs settings, other factor(s)...?

[Synthpopalooza]

Using High causes the picture to blur, which also creates some other artifact colors, this is especially noticeable in lo res modes based out of 160 pixels. Again, plotting some colors on pixels bordering on solid color areas will cause funny things to happen when using this setting. And this is because some TV's and monitors simply cannot display the picture sharply enough.

[+CharlieChaplin]

Well,

 

my Atari 800XL (PAL) is connected to an old 51cm Medion CRT tv. This tv has 2x mono (two speakers, but both output the same audio) and it lacks S-Video and NTSC playback. My A8 does have an S-Video upgrade, but alas this tv does not support it in any way. If I try to playback an NTSC video (with VCR or DVD-player, etc.) on this tv, it shows only black and white and the picture is not centered anymore.The Atari is connected with the tv via the monitor-port (at the Atari end) and the Scart-port (at the tv end).

 

I have to test this tv with Head over Heels and Molecule Man, but as far as I remember (afair), the tv only produced those strange green-red or red-green stripes and no visual colours. The PCS pinball "Das U-Boot" was/is the first game *in Gr.8* that produced real colours on my PAL tv via artefacting (PAL-artefacting)...

 

-Andreas Koch.